The present invention relates to a liquid crystal display panel using a transverse electric field system and including a subpixel for control of a view angle, and an electronic apparatus using the same. More particularly, the invention relates to a liquid crystal panel in which a subpixel for control of a view angle also operates in accordance with a transverse electric field system, and an electronic apparatus using the same.
A liquid crystal display panel is used as a display panel in many electronic apparatuses because the liquid crystal display panel has the features such as light weight, slimness and low power consumption as compared with a Cathode Ray Tube (CRT). The liquid crystal display panel is such that an alignment of liquid crystal molecules arranged in a predetermined direction is changed by application of an electric field to change an amount of light transmitted through a liquid crystal layer, thereby displaying an image on the liquid crystal display panel. With regard to such a liquid crystal display panel, reflection type one, transmission type one, and semi-transmission type one including both the reflection type one and the transmission type one exist. In this case, in the reflection type liquid crystal display panel, an outside light is made incident to a liquid crystal layer, and is reflected by a reflective plate to be transmitted through the liquid crystal layer again to be emitted. Also, in the transmission type liquid crystal display panel, an incident light radiated from a backlight unit is transmitted through a liquid crystal layer.
A longitudinal electric field system and a transverse electric field system are known as those used in a method of applying an electric field to a liquid crystal layer of the liquid crystal display panel. With the liquid crystal display panel using the longitudinal electric field system, an electric field directed approximately in the longitudinal direction is applied to liquid crystal molecules through a pair of electrodes disposed so as to hold the liquid crystal layer between the paired electrodes. A liquid crystal display panel having a Twisted Nematic (TN) mode, a liquid crystal display panel having a Vertical Alignment (VA) mode, a liquid crystal display panel having a Multi-domain Vertical Alignment (MVA) mode or the like is known as the liquid crystal display panel using the longitudinal electric field system. With the liquid crystal display panel using the transverse electric field system, a pair of electrodes is provided in an inner surface side of one of a pair of substrates disposed so as to hold the liquid crystal layer between the paired substrates with the paired electrodes being insulated from each other. Also, an electric field directed approximately in the transverse direction is applied to the liquid crystal molecules. A liquid crystal display panel having an In-Plane Switching (ISP) mode in which a pair of electrodes does not overlap in terms of planar view, and a liquid crystal display panel having a Fringe Field Switching (FFS) mode in which a pair of electrodes overlaps in terms of planar view are known as the liquid crystal display panel using the transverse electric field system.
Of them, in the liquid crystal display panel having the IPS mode, a pair of electrodes composed of a pixel electrode and a common electrode is formed in a pectinate shape so that the paired electrodes are engaged with each other with the paired electrodes being electrically insulated from each other. Also, the transverse electric field is applied across the pixel electrode and the common electrode. The liquid crystal display device having the IPS mode has such an advantage that its view angle is wider than that of the liquid crystal display device having the longitudinal electric field.
In addition, in the liquid crystal display panel having the FFS mode, a pair of electrodes is composed of an upper electrode and a lower electrode. Also, the paired upper and lower electrodes are disposed in different layers, respectively, through an insulating film. A slit-like opening is provided in the upper electrode, and the electric field directed approximately in the transverse direction and passing through the slit-like opening is applied to the liquid crystal layer. The liquid crystal display panel having the FFS mode has been used recently in many cases because the liquid crystal display panel having the FFS mode has an effect that the wide view angle can be obtained and also the image contrast can be improved.
Although as described above, the liquid crystal display panel using the transverse electric field system has the wide view angle, when secret information which is not desired to be peeped is displayed, for the purpose of preventing the secret information from being visibly recognized by anyone else, it is preferable to use the narrow view angle other than the wide view angle. Then, as described in Japanese Patent Laid-Open No. Hei 5-108023, there is known a method of controlling view angle characteristics by adding a liquid crystal panel for control of a view angle to a liquid crystal panel for display. However, this method involves such a problem that the addition of the liquid crystal panel for control of a view angle results in a large increase in thickness of the liquid crystal display panel. In order to cope with this problem, as described in Japanese Patent Laid-Open Nos. 2007-178736 and 2009-222747 (hereinafter referred to as Patent Documents 1 and 2), there is known a method of adding a subpixel for control of a view angle in addition to subpixels for display of Red (R), Green (G) and Blue (B), and controlling a voltage applied to the subpixel for control of a view angle, thereby controlling view angle characteristics.
Here, a structure of the liquid crystal display panel, having the FFS mode, to which the subpixel for control of a view angle disclosed in Patent Documents 1 and 2 is added will now be described with reference to FIG. 9. It is noted that FIG. 9 is a top plan view showing an outline of an array substrate for one pixel of the existing liquid crystal display panel, having the FFS mode, to which the subpixel for control of a view angle is added.
As shown in FIG. 9, one pixel 11H of a liquid crystal display panel 10H is composed of a display region 12H and a view angle control region 13H disposed adjacent to the display region 12H. The display region 12H is composed of three subpixels 16H for display of R, G and B. Also, a color of corresponding one of the pixels is determined based on a mixed color of lights having R, G and B, respectively. The view angle control region 13H includes one subpixel 17H for control of a view angle. An upper electrode 28 of the liquid crystal display panel 10H operates as a common electrode in this case, and is formed over all the pixels. In addition, a low electrode 25 of the liquid crystal display panel 10H operates as a pixel electrode, and is formed every subpixel 16H for display and pixel 17H for control of a view angle.
Also, a first slit-like opening 29H having a dogleg shape is formed in the upper electrode 28 of the display region 12H. An alignment film (not shown) is formed on a surface of the upper electrode 28 and an inner surface of the first slit-like opening 29H. The alignment film is subjected to a rubbing treatment in the same direction as an extension direction (a Y-axis direction in FIG. 9) of a signal line 19. The first slit-like opening 29H is composed of a first subslit-like opening 38 which is inclined with respect to the rubbing treatment direction by +α, and a second subslit-like opening 39 which is inclined with respect to the rubbing treatment direction by −α. A second slit-like opening 30H which extends in a direction vertical to the rubbing treatment direction is formed in the upper electrode 28 of the view angle control region 13H.
As described in Patent Document 2, in the liquid crystal display panel 10H, when a drive voltage is applied across the upper electrode 28 and the lower electrode 25, liquid crystal molecules in the view angle control region 13H are each inclined with respect to a surface of an array substrate. Therefore, although there is no influence of the view angle control in a direct vision direction for the front of the liquid crystal display panel 10H, since the contrast becomes deteriorated due to light leakage in an oblique vision direction, an image displayed becomes difficult to see. As a result, it is possible to offer the view angle control effect.